The present invention relates to a method for determining the oxygen storage capacity of an oxygen store associated with a catalytic converter in the exhaust gas system for an internal combustion engine.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Conventional exhaust gas system include in the flow direction of the exhaust gas a pre-catalytic converter lambda probe arranged in the exhaust gas system upstream of at least a section of the catalytic converter, and a post-catalytic converter lambda probe arranged downstream of the section of the catalytic converter.
The oxygen storage capacity can be determined by initially completely removing oxygen from the oxygen store, thereafter exposing the oxygen store to lean exhaust gas, and integrating the quantity of oxygen introduced per unit time during the exposure with lean exhaust gas based on the air-fuel ratio. The integral is typically determined starting from the onset of the exposure with lean exhaust gas for the purpose of introducing oxygen and ending when the signal from the post-catalytic converter lambda probe crosses a threshold value. When the signal crosses the threshold value, a changeover to exposure with rich exhaust gas is initiated.
The air-fuel ratio in the exhaust gas to which the catalytic converter is exposed is determined based on the output signals of the pre-catalytic converter lambda probe.
However, an offset in the output signal of the pre-catalytic converter lambda probe can have harmful effects: if the lambda probe shows a higher output voltage or a lower output voltage than would otherwise be obtained for the actual air-fuel ratio when using a correctly functioning lambda probe, then the measured oxygen storage capacity is either too high or too low.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for correctly determining the oxygen storage capacity of the catalytic converter even in the presence of such offset in the output signal of a lambda probe.